Control apparatus



ug. 20, 1963 R. L. MILLER ETAL CONTROL APPARATUS Filed Dem` 31. 1958 whymorso@ between its maximum and the time cycle would not remainconstant.,y f It is accordingly `an object of the' present. inventionfto` i 13,101,433 v v Y CONTROL APPARATUS* Robert L. Miller, Hatboro, Roslyn,Pa., assignors'to lator"Company,

Delaware f y FiledDec. 31, 1958, Ser. No. 784,143

y14 Claims. v (Cl. 317-149) Minneapolis, Minn., a corporation of AThepresent invention relates generally vto automatic electric controlapparatus, and relates'specitcally to automatic electric proportioningcontrol apparatus of the timeproportioning type, wherein .a controlaction` `is made f proportional in magnitude to the need therefor mentofthe ratio ofthe control in accordance with the demand arrangementbeing controlled. a

A general object of the present invention is to provide on time to offv'time rimproved :automatic electric control apparatus of the timeproportioning type, by means of which proportional control of a processor other arrangement is eifected in an improved manner by the automaticadjustment of the ratio of the control on time to the control olf timein` accordance with the demand or need for control action of thecontrolled arrangement.

In the'automatic control processes requiring a propertional typeY ofycontrol for proper operation, `numerous processes have been encounteredwhich cannot'vto-lerate so-called throttling control whereintheinstantaneous rate of llow of an agent is made proportional to ameasured value of a controlled condition. Examples of such processes`are certain fuel-red furnaces which cannot tolerate fuel valvethrottling -in the control of fuel vow rateto maintain-aconstant-temperature, v. v As an illustration, itis noted that a widecar-bottom of .the processor other and Rudolphr. Wolf, n., vMinneapolis-Honeywell Reguy Patented Aagh.2o, 1963 q 2 provideimprovedtime proportioning apparatus wherein the time ycycle remainsconstant throughout the range of' operating conditions. i

It is another object of the present `invention to provide an improvedtime proportioning controller yas set forth wherein the time cycle willremain constant ata selected value, but includes means for pre-selectingthe time cycle.

l proportional on-oif pulse signaal.

lay-adjust y Itis a further object ofthe present invention to provide animproved controller as set forth', which is capablelof converting aninput current or `voltage signal into a time A further object of thepresent invention is to provide a time'propontioning controller as setVforth wherein cornpensations for varying conditions in the-signal mayhe performed prior tothe application of vrthe'fsignal to Athe pulsingcircuit.

Still another 'object of the present inventionris4 to provide 'animproved saw-tooth wave rsignal generator; In accomplishing these andother objectspthere has beenv provided, in accordance with the presentinvention, a

saw-tooth Wave generator wherein a charging capacitor is charged from 'aconstant current source, such as it Vrepresented by a series transistor,to 'produce a linear ramp function. The ramp functionv is applied tocontrol the cathode grid bias on a vacuum tube which in'turn p controlsthe operation of a relay. One pair of contacts on the aforesaid relayeffectively shorts out the charging capacitor at the 'end Vof thepre-set time-cycle thus forming the saw-tooth wave; The sawatooth wavethus developed is applied as bias tothe cathode of a second vacuumtubej. which has a second relay connected in series with the Ianodecircuit thereof. The controlling signal is applied i asgridlrbias tothesecond vacuum tube thereby controlling furnace must be tired at maximumYratte, when heat is .f

v input to the furnace in pulses, the'ratio, during any given period, ofvalve maximum open or onv time to'v vthe total vperiod of time bei-ngmade proportional to thef need for heat as indicated by the measuredfurnace tern-y perature. :By `deiinition, the total. time '-is equalfto' theV valve maximum open or fon time plus the" valve minimuml openor off time.-

Time proportioning :control is also required for the con-v trol vof "thetemperature of electric furnaces Where it is not feasible to vary thefurnace-heater energizing current where, therefore, the heating currentmust'f-fully b e-"on when heat is` called for-.1f The control' apparatus'of the present invention fulfills v ing or regulating the furnace heatinput'y by' varying. .the`

cordance with the furnaceiload demand.

In accordance iwith previous eiforts' at 'accomplishing' atime-proportional control, wherein rlesorthas been hadv the use .ofeither a thermal bridge or theicharging characteristic of a capacitonithas been found that since bothy of these "techniques result" in',apparatus that followsan exponential curve, for varying conditions ofoperation? vratio of heating cu-rrentfon time to the total time in ac-`this requirement by proportion the conductivity o fl the second vacuumtube and, hence, the oper-ation of the second relay as a proportionalfuncf tion of Vthe time-cycle determined by the aforementionedsawftoothwave.

Avbetter understanding of l the present invention, and

`ating characteristics fof the this invention maybe had from. the'following detailed .description when `read` inl connection with theaccompanying Vdrawings in which:`

of a control system' embodying FIG. l is an illustration FIG. 2 shows aset of curves representative of the operwith the present invention.

l 1 Referring now to the drawing in moreidetail thereis shown in FIG. 1-a 4furnace 2 having a flame nozzle 4 which feeds fuel tothe furnacefrom 4a' fuel supplymline Gppast a control Vvalve 8. Thevalve 8 may beanyone of a number of suitable valves which may be operated be.

l. tween a fully opened and-a minimurnopened or closedv position byoperation of a signal responsive valveactuatorl I p 10. The temperature1in the furnacev is sensed by a thermominimum'or oit valves, 'and couple12. The thermocouplesignalI is-.applied as input.

to a suitable instrument'14 which maybe-any one o f ya number of)differenttypes of instruments. The instr-ufI ment 14 may, for example,be means forv controlling and amplifying the derived signal. Theycontrolling 'function may, of course, include such characteristic`adjustments of `the-signal as are frequently found in electric or other,-..pro;cess controllers. These functions are .identified asV rarte,reset. and proportional fband adjustments of the signal. xIn the event.that the instrument14 is a contro-ller, as set forth herein, theoutput' signal will beV av` current signal applied to the terminal `16.The `current at terminal 16 is applied across a variable resistorA 18to.v

I produce -a voltage signal at the terminal 20. Thispvoltage signal willbe lapplied as input signal or controlling signals to they timeproportioning circuit of the present invention.'

\This time proportioning circuit includes a directeur- I rent powersupply, represented byQthe battery 22. The

manitas,

control system in accordance positive terminal, of the battery. 22 isconnected through a irst limiting resistor 24, throughy a slidewireresistor 26, and a second limiting resistor 28, thence to the negative.terminal of the battery `22.,` The positive terminal of the battery 22is also connected through a biasing A second and normally closedfcontact42 of the switch 38" is arrangedjto. short-'circuit the .capacitor `i0through a small current-limitingresistor 44. yThe positivetermi'nal offthe battery 22 is also connected through a coupling resistente. thecontrol-'gridof a'vacuum Itube 48.

` The anode'of thetube y48 is connected thronghthe operating .coil .of avrelay 50 t0 a suitable power supply 52. Ar'timeconstant determiningcapacitor 54 is connected in parallel with the relay coil 50. Thecathode A'of Vthe tube-t8 is connected through the cathode bias resistor56 and itsby-pass capacitor, to the bus `58 which is in 'turn connectedtothe junction between the movable element or the switch 38 and thecapacitor y4t). Thus, this bus carries the ramp [function :generated bythe `foregoing circuitry. The power source ,52, is also referred to thebus l58.' f j A second vacuum tube' 60 has its cathode connected througha pair of series connected resistors-62 and'64 to the bus 58. Here,again, there is provided the usual cathode by-pass capacitor. The anodeott the tube 60 is connected through the operating coil olf a secondrelay 66 to the power source 52. The coil 66 is also provided with atime constant determining capacitorv .68'. The junctionrbetween the tworesistors 62 and l64'in the 'cathode 'or' the'tube is connected througha pair of normally closed contacts to the bus 58. rIhus when thecontacts are `'closed the resisto-1564l isshorted out. A neon lampindicator 72v is connected through a kpair of normally vopened contacts7 4 acrossI the power supply 5 2. The con-` ytacts 70 and74 are both`operated by the relay 66. The gridwof the vacuum tube 60 is connectedthrough a coupling resistor 76 tothe terminal 20 which it will berecalled has a control signal supplied thereto.

' A power source78 is connected to energize the valve actuatorandwhenever the circuit interconnecting the power source 78 and thevalve actuator is completed; In order for thisv circuit to beV completedtwo separate contacts Vvmust both be closed, the irst 'of 'thesecontacts 80 4is arranged toy berclosed, whenever the relay 66 is 4 Whenthe relay y50 is deenergized the contact 36 or the switch 38 is openedand the contact Y42 is closed, there` by short -cirouiting the capacitor40. This substantially instantaneously drops the potential on the bus 58to the point whereat the tube 48--again begins to conduct sufricientlyto energize the relay 50. The `foregoing operation produces. on the bus`58a voltage characteristic' suchas represented by the curves .ort FIG.2. In that ligure,

curvefa is selected to yrepresent the saw-tooth waveV generated by thecooperation lof VVthe toregoingcircuit elements, withk the slide 34- atsome middle value along vthe slidewire 26; while curve b shows acorresponding characteristic, but with a shorter charging time for thecapacitor -40 .due to {higher cur-rent flow through the transistor 32..Similarly curve c shows a corresponding` current Yilow through thetransistor 32. These last two mentioned curves of course represent theoperation of theL circuit with the slider 34 at'dilerent positions alongtheA slidewire resistor 26.l It may be noticed thatrthe forwar-d slopeor ramp function of these curves is substantially linear with respect totime and the drop-olf or dis.

charge of the capacitor 40` is substantially instantaneous.-

It should also be noted that the time during which the relay 50 isdeenergized is extremely short. This may be seen when it is realizedthat as soon as the capacitor 40 has discharged to the point whereat thebias is reestablished between-the grid and the cathode of the tube 48,the tube 48 will immediately begin heavy conduction again. l

The saw-tooth voltage characteristic thus generated is applied as biasto the cathode of the second tube`60. This bias is compared with thesignal `applied to the grid as input control signal from the terminal20. So long ing fuel to liow into the lfurnace through the nozzle 4; nWhen, however, the bias on the bus 58 has vprogressed as the biasapplied to the grid lfrom the terminal 20 is suiciently higher than thecathode bias applied ifrom the bus 58, the tube 60 will be in such astate of conductionV tha-t the second relay l66 fwill be energized,closing the contact A80. During this time, oli' course, the contacts 82are closed. Under theseconditions, power trom the source 78` is appliedto the valve actuator 10, thereby opening the valve 8 to its maximumposition, allowsufficientlyv far up the [forward slope that thedifferential bias betweenthe cathode and grid of the tubey60'is suchlined with respect to the curves a, b, or c, will of suitablyenergized. Thesecond of the contacts 82 is arranged to be closed whenever the relay.5U is suitably energized. f v' '-Assume that al1-of the switch contactsare'moved to the. position shown. Theltube 48 will be biased intomaximum conduction. When that happens, the coil 50` of Thiscurrentappears as a charging current tor the capacitor 40.' Since thecurrent through the transistoris constant, the charge on the capacitory4)` buil-.ds upv linearly v f withtimefA .Asthe' change on thecapacitor 40 builds up, the grid toV cathode bias relationship otfthetube 48 is diminished until the current drawn A-by the' tube 438 isinsuicient to maintain ythe enengizati'on of the relay '50;

that the Vconductivity of the tube is 'insufficient to maintain theenergization of therelay 66,l that relay drops out, opening the contact80. -rllhis value may be represented bythe line d through the curves ofFIG. 2. In FIG. 2' this lined is illustrated as being that about the 50%on time position. The relative position of the.

course be determined by the magnitude of the signal applied totheterminal 20 to the grid of the tube 60. It the. signal applied from theterminal 20 is lgreater, then the line d will appear higher withlrespect to the curves a, b, .or c, thus indicating a langer percent ontime, whereas ir the signal applied trom the terminal 20 were lower theline d would be lower with respect to the curves a, b, :or c. indicatinga lower percent on time. Y.

ySince it is characteristic *of` relays that the current level necessarytol cause the relay to be energized .is somewhat greaterthan the currentlevel necessary to hold anyv given position of thefslider34= along theslidewire 26, the current through the transistor will befconstant.

L normally closedA contacts. 70.

tin an energized condition, that is, the pickup current is. greater thanthe drop out current, there appears an area in the lower percent ontimeA region during which control rnay nnot be exercised. However, inorder to overcome this apparent' inherent characteristics of relays, abias compensation is inserted. Inasmuch as there is alwayssome currentowing through the tube 60 from the-source 5-2. a measure or cathode biasfis obtained by the :flowv of this current through-the resistor 62, andthe through thev tube-60 is sufficient. to cause the relay 66 Wheneverthe current to be' energized, the normally closedcontact y76 is opened.

This, then causes the cathode bias to be'established'across` 4 the sum'-of the two series resistors 62 and 64, producing a Ict'nrrespondingshift in the magnitude of the `cathode bias. 'Iliis shitt in the cathodebias due to the opening of the relay' contacts 70, is of a magnitude andin a direction compensate [for the aforementioneddifferential inthepickup and Idringt out current of the relay 66. Thus, per-` cent on timecan be controlled` substantially `down to Zero percent on time. ,Q

I'Ihe glow-tube or 'other indicating. device 72` is connected inacircuit arranged to be interrupted'byr the normally open contact 74 ofthe relay 66. Whenever the relay -66- is energized so that the valve [8is open admitting fuel into the furnace 2, the Yrelay contact 74 is`closed completing the circuit to the glow tube 7 2, causing the same tobe lit as an indication of the opened condition of the yalve 8.

The arrangement with the two sets of relay contacts 80 andSZ'connectedin series and operated separately by the two relays 50 and 66,respectively, constitutes a fail safe sfeature. `Both relays must beenergized in order for the valve actuator to be energized. Thus anyevent which would cause the iirst. tube 48 to cease conductingsuiiiciently to energize theA relay t) would also cause the circuit tothe `valve actuator to be opened.

It will be appreciated that while theinvention has been described, asincluding the two vacuum tubes r48` and 60, other suitable currentcontrolled devices may be sub` stituted therefor without departing fromthe spirit and scope of the present invention. apparent that` suitablyarranged transistors can be substituted for the tubes 48 and 66'.Similarly, other functions than a valve actuator may be controlledvbythe periodic pulsing of the power rfrom the source 78.

Thus it may be seen that there has been provided in accordlanceV withthe present invention an improved time proportioning controller whereinthe time cycle remains constant at a selected naine irrespective of theoperating range of the system and which includes a'novel` saw-tooth wavegenerator.

What is claimed is:

l. A linear sawtooth Wave signal generator comprising a chargingcapacitor, a sounce of electrical energy, a transistor connected inseries with said capacitor and said source, means [for selectivelybiasing'said transistor to produce `a predetermined constant currenttherethrough whereby to charge said capacitor 4at a linear rate, meansdening a dischargecircuit for'said capacitor, switch means operative inresponsetothe build-up of a charge It will, of course, `be

'6 i `4. A linear sawtooth wave signal generator comprising a changingcapacitor, a constant current circuit including a transistor and meansfor applying electrical energy thereto, a switch means for selectivelyconnecting', said capacitor tosaid constant current circuit whereby todevelop a charge' on said capacitor, a relayv having an operatingtwinding, means for applying 'an energizing current to said operatingWinding, a current control/means for controlling the flow of energizingcurrent through said winding, said current control means being connectedto said capacitor to deener-gize said relay in response to thedevelopment of a charge on said capacitor to a predetermined level,saidswitch means being a set of conf g tacts on saidv relay andoperative upon deenergiz'ation of saidrelay to `disconnect saidcapacitor from saidjconstant current circuit and to connect saidcapacitor to `a discharge circuit, said current control meansbeingfurther operative to reenengize said relay in response to the dischargeorf said capacitor, and output means connected to said capacitor. l

5. A linear sawtooth wave generatorA comprising a charging capacitor, asource of electrical energy, a transistor connected in series with saidcapacitor and said source, biasing means connected to said source 1to1derive therefrom a biasing signal for selectively biasing saidtransistor to produce a predetermined constant current therethroughrwlhereby to charge said capacitorat a linear rate, means delining adischarge circuit forsaidcapacitor, switch means operative in responsetothe build-upfof a a charge on said capacitor to a predetermined levelto disconnect said :capacitor from said transistorand to connect saidcapacitor to said dischange circuit, said switch ymeans being [furtherkoperative to reconnect said capacitorto said transistor upon dischargeof said capacitor, and output means connected to said capacitor.'

' control 'apparatus comprising,

16. A time proportioning in combination, means :for generating alinear'sawtooth wave voltage signal, a current control device, means tor onsaid capacitor to a 'predetermined llevel to disconnect said capacitorfrom said transistor and to connect said capacitor to said dischargecircuit, said switch'means being further operative to reconnect saidcapacitor to said transistor upon discharge of said capacitor, andoutput means connectedr to said capacitor.

2. A linear sawtooth wave signal generatorcornprising a chargingcapacitor, a constant current circuit including a transistor, switchmeans-tor selectively connecting said capacitor to said circuit wherebyto develop a charge on said capacitor, means defining a dischargelcircuit tor said capacitor, means responsive to the development of saidchangel on said capacitor to a predeterminedl level to actuate saidswitch means to disconnect said capacitor trom said constant currentcircuit and to connect said capacitor to said discharge circuit, saidcharge responsivey means being further operative'to reconnect saidcapacitor" to said constant current circuit upon discharge of saidlcapacitor, and output means connected to` said capacitor.

3. A sawtooth wave signal generator as set forth inv by to adjust thecyclic repetition rate of the generated y sawtooth wave signal.

applying a control signal to said current control device, means forapplying said sawtooth wave signal as bias to said current controldevicev for cyclic comparison with said `control signal whereby tocontrol the ilow of current through said control device on a timev cycledetermined by the repetition rate of said sawtooth signal and for aproportionate time during each cycle determined by the relativemagnitude of said control signal, and output operation control meansresponsive to the current ow through said current :control means. v

7. A time proportioning control apparatus comprising means forgenerating alinear sawtooth wave voltage signal, `a relay having anoperating winding, means for applying an energizing current to saidoperating winding, v

a current control means for controlling the flow of enera control signalto said current control means, means for applying said sawtooth Wavesignal as bias to said current control means for cyclic comparison withsaid control signal lwhereby to control the flow of energizing currentthrough said operating windingon a time cycle ydetermined by therepetition rate of said sawtooth wave signal for energizing said relayduring at Ileast a portion 'orfy e'achrcycle, said portion beingdetermined by the rela'- tive magnitude of said control signal, and anoutput means responsive to the operation of said relay.

8. A Vtime proportioning control apparatus comprising means forgenerating alinear sawtooth wave voltage signal; said means including aconstant current circuit includin-g a transistor, a charging capacitor,switch means for `selectively connecting said capacitor to said constantcurrent circuit whereby to develop a charge on said capacitor, meansresponsive to the development of said charge on said capacitor to apredetermined level to actuate said switch means to disconnect-saidcapacitor from said constant current circuit and to connect saidcapacitor to a discharge circuit, said charge responsive means being"further operative to reconnect saidy capacitorto said constant currentcircuit upon discharge of said capacitor; a relay having an operatingWinding, a current control means for controlling the ow ofV energizingcurrent through, said winding, means for applying a control signal meansbeing operative to compare said control signal and said bias signal andto effect enengization ont said relay during a portion of each cycle ofsaid sawtooth v wave signal dependingupon the relative magnitude ofVsaid control signa-l.'

9j. A time proportioning control apparatus comprising p means includinga capacitor and a constant current charge ing circuit therefor forgenerating a linear sawtooth wave signal, a relay vhaving an operatingwinding, means `for applyingan energizing current to said operatingwinding, a current control means for controlling the flow of energizingcurrent through said Winding to control the operation of said relay,means cfor applying a control signal to said current control means,means for applying said sawtooth 'wave' signal as bias on said currentcontrol means, -1 said control means being operatiye to compare saidcontrol signal and said bias signal and to effect energization of saidrelay during a portion of each cycle ofe said sawtooth wave signaldepending upon the relaltive magnitude olf said control signal. f

10. A time proportioning control apparatus comprising means including acapacitor and a constant current charging circuit therefor for.generating a linear sawtooth wave signal, a relay having an operatingwinding, means for applying an energizing current to said operatingWinding, current control means for controlling the ilow of energizingcurrent through said winding, said current control means comprising aVacuum tube having a cathode, con trol-grid and anode, said relaywinding being connected in the anode circuit of s aid tube, means forapplying a control signal to said grid of said 'vacuum tube, means foraimg'lyingy said sawtooth fwlave :signal as `bias on 4said cathode, saidvacuum tube being operative to compare said control signal with saidbias signal to effect an enerf gization of said relay during a portionof each cycle of said sawtooth lWave signall depending upon themagnitude or said control signal.

ll.y A time proportioning control apparatus comprising means rforgenerating a linear sawtooth Wave signal, said meansincludingacapacitoigy a constant current charging circuit thereforincluding a transistor, means for connecting said capacitor to saidcharging circuit to develop a charge on said capacitor, a relay havingan operating lwinding, signal responsive means connected to control theiiow of energizingcurrent through said winding, said relative sign-alresponsive means being operative in response to the development of acharge on` said capacitor to a predetermined ilesfel to deenergize saidrelay, switch means included insaid relay operative upon deenergizationor said relay A,to disconnect of said capacitor'ifrom said chargingcircuit and to connect saidpcapacitor to a discharge circuit, saidsignal responsive means being further i operative upon discharge of saidcapacitor to reenergize said relay and thereby to reconnect saidcapacitor to said charging circuit; a second relay having an operatingWinding; current control means for controlling the flow of energizingcurrent through said operating Winding of said second relay; means ttorapplying a control signal to said current control means; means* forapplying said developed sawtooth wave signal -as bias on said currentcontrol means; said current control means being operative to comparesaid control signal with said bias signal whereby to eect energizationof said second relay during a portion ofleaich cycle of said sawtoothwave signal depending upon the relative magnitudeoff said controlsignal.

|12, The invention as set [forth in claim 11 and characterized by theaddition of means responsive to the energization of said second relayfor modifying the bias on said current control means.

'means for generating a sawtooth Wave signal, a relay having a signalresponsive element, a control member for controlling a signal Vappliedto said signal responsive ele? ment, means rfor applying a controlsignal to said convtrol member, means for applying said sawtooth Wavesignal as bias to said control member, said control member beingoperative to compare said control signal and said bias signal to effectan actuation of said relay during a portion of each cycle of said lbiassignal depending upon the relative magnitude of said control signal.

References Cited in the iile of this patent UNITED STATES PATENTS FrankDec. 16, 1958

6. A TIME PROPORTIONING CONTROL APPARATUS COMPRISING, IN COMBINATION,MEANS FOR GENERATING A LINEAR SAWTOOTH WAVE VOLTAGE SIGNAL, A CURRENTCONTROL DEVICE, MEANS FOR APPLYING A CONTROL SIGNAL TO SAID CURRENTCONTROL DEVICE, MEANS FOR APPLYING SAID SAWTOOTH WAVE SIGNAL AS BIAS TOSAID CURRENT CONTROL DEVICE FOR CYCLIC COMPARISON WITH SAID CONTROLSIGNAL WHEREBY TO CONTROL THE FLOW OF CURRENT THROUGH SAID CONTROLDEVICE ON A TIME CYCLE DETERMINED BY THE REPETITION RATE OF SAIDSAWTOOTH SIGNAL AND FOR A PROPORTIONATE TIME DURING EACH CYCLEDETERMINED BY THE RELATIVE MAGNITUDE OF SAID CONTROL SIGNAL, AND OUTPUTOPERATION CONTROL MEANS RESPONSIVE TO THE CURRENT FLOW THROUGH SAIDCURRENT CONTROL MEANS.